Particulate compositions of particulate metal and polymer binder

ABSTRACT

A particulate composition wherein each particle thereof includes a first metal (e.g., tungsten), an optional second metal (e.g., tin), and a polymer binder (e.g., thermoplastic polyvinyl alcohol) is described. The first metal has a particle size of less than or equal to 10 μm, and the second metal has a particle size of less than or equal to 20 μm. The polymer binder is typically present in each particle of the particulate composition in an amount of from 0.5 to 2.5 percent by weight, based on the total weight of the particulate composition. The particulate composition has an average particle size of 25 to 300 μm, and is free flowing. The particles of the particulate composition are preferably substantially spherical. Also described is a method of preparing the particulate composition by means of spray drying. The particulate compositions may be used to prepare molded articles, such as frangible projectiles (e.g., frangible bullets).

FIELD OF THE INVENTION

The present invention relates to particulate compositions that include one or more particulate metals (e.g., tungsten and tin) and a thermoplastic and/or thermosetting polymer binder. Each particle of the particulate composition has substantially the same proportions of metal and polymer binder. The present invention also relates to a method of preparing such particulate compositions by means of spray drying, and to molded articles prepared from such particulate compositions (e.g., frangible projectiles).

BACKGOUND OF THE INVENTION

Frangible projectiles, such as frangible bullets, are designed to fragment upon impact with an object of sufficient density (e.g., a human being, an animal or a wall). Relative to standard non-frangible bullets, frangible bullets are capable of imparting increased tissue and internal organ damage (i.e., improved take-down capacity) while at the same time minimizing the risk of the bullet passing intact through an intended target and hitting or seriously injuring an innocent bystander. In addition, if a frangible bullet misses its intended target and hits a wall, it is less likely to pass through the wall intact and seriously injure or damage an unintended object on the other side of the wall. Frangible bullets also find use in indoor firing ranges, because they fragment upon hitting the back wall behind the targets, thus minimizing the risk of ricochets seriously injuring personnel on and behind the firing line.

Bullets have been and continue to be fabricated from lead, due in part to the ease with which lead can be shaped and molded, its high density, its availability and relative low cost, and its softness which minimizes damage to the interior of a gun barrel from which the lead bullet is fired. However, there are environmental and health concerns associated with lead projectiles. Lead projectiles left in the field (e.g., a marsh) can lead to increased lead levels in the ecosystem and the food chain. The use of lead projectiles in indoor firing ranges raises health concerns associated with lead dust and vapors that may be formed when lead bullets hit the down range back wall.

As such, the development of lead-free projectiles, including lead-free frangible projectiles is desirable. However, to better approximate the feel (e.g., kick-back upon firing) and trajectory associated with lead projectiles, it is desirable that lead-free projectiles have a density that substantially approximates that of the lead projectiles being replaced.

Frangible projectiles are typically fabricated from one or more metal powders (e.g., tungsten and tin powders) that are compressed together with the optional application of elevated temperature. However, maintaining two or more metal powders in a desired proportion prior to molding of the projectile can be problematic due to, for example, separation of the metals resulting from handling related vibrations.

Frangible projectiles having sufficiently high densities, at least approximating those of lead projectiles, may be obtained through the use of metal powders having small particle sizes (e.g., average particle sizes of less than 20 μm). However, there are typically handling and safety concerns associated with metal powders having small average particle sizes of, for example, less than 20 μm. Metal powders of such small particle size may not flow properly when being fed into a projectile mold, and may clog the feed port thereof. There may be increased explosion hazard and respiratory injury concerns associated with the use of small particle size metal powders in the production of molded articles there from, such as frangible projectiles.

It would be desirable to develop particulate compositions (e.g., from which frangible projectiles may be prepared) that are not prone to separation of different metals and/or different particle size metals used therein. In addition, it would be desirable that such newly developed particulate compositions contain small particle size metal powders, but not be subject to the handling and safety concerns that are typically associated with small particle size metal powders.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided, a particulate composition comprising:

(a) a first metal selected from the group consisting of tungsten, tungsten carbide, ferro-tungsten, bismuth, stainless steel, tantalum, molybdenum, combinations thereof, and alloys of at least two metals thereof, said first metal having an average particle size of less than or equal to 10 μm;

(b) optionally a second metal selected from the group consisting of tin,

 zinc, iron, copper, aluminum, combinations thereof, and alloys of at least two metals thereof, said second metal having an average particle size of less than or equal to 20 μm;

(c) a binder selected from the group consisting of thermosetting resins, thermoplastic resins and combinations thereof,

wherein each particle of said particulate composition substantially comprises,

said first metal in an amount of from 30 percent by weight to 99 percent by weight, based on the total weight of said particulate composition,

said second metal in an amount of from 0 percent by weight to 70 percent by weight, based on the total weight of said particulate composition, and

said binder in an amount of 0.5 percent by weight to 2.5 percent by weight, based on the total weight of said particulate composition, said particulate composition has an average particle size of from 25 μm to 300 μm, and said particulate composition is substantially free flowing. In a preferred embodiment, the particles of the particulate composition are substantially spherical.

In accordance with the present invention, there is also provided a method of preparing a particulate composition comprising:

(a) forming a substantially homogenous particulate metal mixture comprising,

-   -   (i) a first metal selected from the group consisting of         tungsten, tungsten carbide, ferro-tungsten, bismuth, stainless         steel, tantalum, molybdenum, combinations thereof, and alloys of         at least two metals thereof, said first metal having an average         particle size of less than or equal to 10 μm, and     -   (ii) optionally a second metal selected from the group         consisting of tin, zinc, iron, copper, aluminum, combinations         thereof, and alloys of at least two metals thereof, said second         metal having an average particle size of less than or equal to         20 μm,     -   said first metal being present in said particulate metal mixture         in an amount of from 30 percent by weight to 100 percent by         weight, based on the total weight of said particulate metal         mixture, said second metal being present in said particulate         metal mixture in an amount of from 0 percent by weight to 70         percent by weight, based on the total weight of said particulate         metal mixture, and said particulate metal mixture being         substantially dry;

(b) preparing a slurry comprising,

-   -   (i) said homogenous particulate metal mixture,     -   (ii) water,     -   (iii) a binder selected from the group consisting of         thermosetting resins, thermoplastic resins and combinations         thereof, and     -   (iv) optionally a defoamer,     -   wherein said slurry contains,     -   said first metal in an amount of from 24 to 89 percent by         weight, based on the total weight of said slurry,     -   said second metal in an amount of from 0 to 63 percent by         weight, based on the total weight of said slurry,     -   water in an amount of from 10 to 25 percent by weight, based on         the total weight of said slurry,     -   binder in an amount of from 0.4 to 2.2 percent by weight, based         on the total weight of said slurry, and     -   defoamer in an amount of from 0 percent by weight to 0.05         percent by weight, based on the total weight of said slurry; and

(c) passing said slurry through a spray drier, thereby forming said particulate composition,

wherein each particle of said particulate composition substantially comprises,

said first metal in an amount of from 30 percent by weight to 99 percent by weight, based on the total weight of said particulate composition,

said second metal in an amount of from 0 percent by weight to 70 percent by weight, based on the total weight of said particulate composition, and

said binder in an amount of 0.5 percent by weight to 2.5 percent by weight, based on the total weight of said particulate composition,

said particulate composition has an average particle size of from 25 μm to 300 μm, the particles of said particulate composition are substantially spherical, and said particulate composition is substantially free flowing.

The present invention also provides molded articles, such as projectiles (e.g., bullets and frangible bullets) that are fabricated from the particulate compositions of the present invention, and/or particulate compositions prepared by the method of the present invention.

Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as modified in all instances by the term “about.”

DETAILED DESCRIPTION OF THE INVENTION

The first metal of the particulate composition of the present invention may be selected from tungsten, tungsten carbide, ferro-tungsten, bismuth, stainless steel, tantalum, molybdenum, combinations thereof (e.g., physical mixtures of two or more metals thereof, and alloys of at least two metals thereof. In a preferred embodiment of the present invention, the first metal comprises tungsten and optionally one further metal selected from tungsten carbide, ferro-tungsten, bismuth, stainless steel, tantalum, molybdenum, combinations thereof, and alloys of at least two metals thereof. In a particularly preferred embodiment, the first metal substantially comprises tungsten.

The first metal has an average particle size selected from positive values that are less than or equal to 10 μm (microns). Typically, the first metal has an average particle size that is greater than or equal to 1 μm and less than or equal to 10 μm (e.g., from 2 μm to 9 μm, or from 3 μm to 8 μm).

As used herein and in the claims, unless otherwise indicated, the term “average particle size” relative to the first and second metals is determined in accordance with ASTM B 822 using a MICROTRAC particle analyzer, commercially available from Microtrac, Inc.

The first metal may be present in each particle of the particulate mixture of the present invention in an amount of less than or equal to 99 percent by weight, typically less than or equal to 95 percent by weight, and more typically less than or equal to 90 percent by weight, based on the total weight of the particulate composition. The first metal may also be present in each particle of the particulate mixture in an amount of greater than or equal to 30 percent by weight, typically greater than or equal to 50 percent by weight, and more typically greater than or equal to 65 percent by weight, based on the total weight of the particulate composition. The first metal may be present in each particle of the particulate composition in amounts ranging between any combination of these upper and lower values, inclusive of the recited values. For example the first metal may be present in each particle of the particulate composition in an amount of from 30 to 99 percent by weight, typically from 50 to 95 percent by weight, and more typically from 65 to 90 percent by weight, the percent weights being based on the total weight of the particulate composition.

The second metal of the particulate composition of the present invention may be selected from tin, zinc, iron, copper, aluminum, combinations thereof (e.g., physical mixtures of two or more metals thereof), and alloys of at least two metals thereof. In a preferred embodiment, the second metal comprises tin and optionally at least one metal selected from zinc, iron, copper, aluminum, combinations thereof, and alloys of at least two metals thereof. In a particularly preferred embodiment, the second metal substantially comprises tin.

The second metal has an average particle size selected from positive values that are less than or equal to 20 μm. Typically, the second metal has an average particle size that is greater than or equal to 2 μm and less than or equal to 20 μm (e.g., from 3 μm to 18 μm, or from 5 μm to 15 μm).

The second metal may be present in each particle of the particulate composition of the present invention in an amount of less than or equal to 70 percent by weight, typically less than or equal to 50 percent by weight, and more typically less than or equal to 35 percent by weight, based on the total weight of the particulate composition. The second metal may also be present in each particle of the particulate mixture in an amount of greater than or equal to 0 percent by weight, typically greater than or equal to 5 percent by weight, and more typically greater than or equal to 10 percent by weight, based on the total weight of the particulate composition. The second metal may be present in each particle of the particulate composition in amounts ranging between any combination of these upper and lower values, inclusive of the recited values. For example the second metal may be present in each particle of the particulate composition in an amount of from 0 to 70 percent by weight, typically from 5 to 50 percent by weight, and more typically from 10 to 35 percent by weight, the percent weights being based on the total weight of the particulate composition.

The second metal is an optional component of the particulate composition of the present invention. In preferred embodiments, the particulate composition includes both the first metal and the second metal. The ratio of the weight of the first metal to the second metal, in the particulate composition, may range between any combination of those percent weights that are recited previously herein with regard to the first and second metals. Preferably, the first metal is present in the particulate composition in a weight amount that is greater than that of the second metal. For example, the particulate composition may contain a weight ratio of the first metal to the second metal of: 10 to 1; 5 to 1; 4 to 1; 3 to 1; 2 to 1; or 1.5 to 1. In a preferred embodiment of the present invention, the particulate composition (and more particularly, each particle of the particulate composition) contains a weight ratio of the first metal (e.g., tungsten) to the second metal (e.g., tin) of 4 to 1.

In an embodiment of the present invention the particle sizes of the first and second metals are each selected, in addition to and accordance with the ranges as recited previously herein, such that the second metal has an average particle size that is greater than the average particle size of the first metal. For example, the particle sizes of the first and second metals may each be selected such that the second metal has an average particle size of 10 μm greater, 7 μm greater, 5 μm greater, or 3 μm greater than the average particle size of the first metal. The second metal, for example, may have an average particle size of 20 μm while the first metal has an average particle size of 10 μm. Alternatively, the second metal may, for example, have an average particle size of 12 μm while the first metal may accordingly have an average particle size of 2 μm, 5 μm, 7 μm or 9 μm.

The binder of the particulate composition is a polymer binder, and more particularly an organic polymer binder. The binder may be selected from thermosetting resins and/or thermoplastic resins.

If the particulate composition is prepared by spray drying of a liquid composition, such as an aqueous composition (which will be discussed in further detail herein), it is preferable that the binder material be dispersible or miscible in the medium of the liquid composition. Such dispersibility or miscibility in water may be achieved by known means, which include, but are not limited to: selecting an appropriate polymer backbone; selecting or introducing terminal and/or pendent functional groups into/onto the polymer; and the use of dispersing aids, such as surfactants and/or cosolvents. For example, when the liquid composition that is spray dried is an aqueous composition, the presence of pendent and/or terminal hydroxyl and/or carboxylic acid groups (optionally salted with bases, such as amines) may enhance dispersibility of the polymer resin in the aqueous medium, as is known to the skilled artisan.

As used herein and in the claims, with regard to the binder, the term “thermosetting resins” and similar terms means plastic resins having a three dimensional crosslinked network resulting from the formation of covalent bonds between chemically reactive groups (e.g., active hydrogen groups and free isocyanate groups or oxirane groups). Thermosetting resins from which the binder may be selected include those known to the skilled artisan, e.g., crosslinked polyurethanes, crosslinked polyepoxides and crosslinked polyesters.

As used herein and in the claims, with regard to the binder, the term “thermoplastic resin” and similar terms means a plastic resin that has a softening or melting point, and is substantially free of a three dimensional crosslinked network resulting from the formation of covalent bonds between chemically reactive groups (e.g., active hydrogen groups and free isocyanate groups). Examples of thermoplastic resins from which the binder may be selected include, but are not limited to, polyvinyl alcohol, poly(C₂-C₅-alkylene glycol), hydroxyalkylcellulose, polyacrylate, polymethacrylate, polyurethane, polyolefin, polyester, polyamide and combinations thereof. In a preferred embodiment of the present invention, the binder is thermoplastic polyvinyl alcohol.

The binder may be present in each particle of the particulate mixture of the present invention in an amount of less than or equal to 2.5 percent by weight, typically less than or equal to 1.3 percent by weight, and more typically less than or equal to 0.9 percent by weight, based on the total weight of the particulate composition. The binder may also be present in each particle of the particulate mixture in an amount of greater than or equal to 0.5 percent by weight, typically greater than or equal to 0.6 percent by weight, and more typically greater than or equal to 0.7 percent by weight, based on the total weight of the particulate composition. The binder may be present in each particle of the particulate composition in amounts ranging between any combination of these upper and lower values, inclusive of the recited values. For example the binder may be present in each particle of the particulate composition in an amount of from 0.5 to 2.5 percent by weight, typically from 0.6 to 1.3 percent by weight, and more typically from 0.7 to 0.9 percent by weight, the percent weights being based on the total weight of the particulate composition.

Each particle of the particulate composition of the present invention substantially comprises each of the first metal, the second metal and the binder in the amounts as recited previously herein. Variations in composition between each particle are typically less than ±3 percent by weight, and more typically less than ±1 percent by weight, based on the weight of the particulate composition. The substantial uniformity of composition between each particle of the particulate composition provides for improved quality control with regard to molded articles prepared from the particulate compositions of the present invention. For example, projectiles, such as frangible bullets, prepared from the particulate compositions of the present invention have minimal variations in weight and performance properties (e.g., trajectories and frangibility) amongst individual projectiles and between lots of projectiles.

The particulate composition of the present invention may optionally include other components, such as processing aids. Typically, such other optional components are present in amounts of no more than 10 percent by weight, based on the total weight of the particulate composition. When prepared by spray drying, for example, the particulate composition may optionally further include defoamers and/or surfactants in amounts that are typically less than 1 percent by weight, based on the total weight of the particulate composition.

The particulate composition is substantially free flowing. As used herein and in the claims, “substantially free flowing” means that the particulate compositions have handling properties that allow them to be transferred controllably and at reproducible rates, for example into a mold, such as a mold for preparing a frangible projectile. More particularly, particulate compositions according to the present invention typically have positive (i.e., greater than zero) Hall flow values of less than or equal to 35 seconds/50 grams, preferably less than or equal to 30 seconds/50 grams, and more preferably less than or equal to 25 seconds/50 grams (as determined in accordance with ASTM B 213). The Hall flow values of the particulate composition of the present invention are preferably as low as is possible. Generally, the Hall flow values of the particulate composition are greater than or equal to 8 seconds/50 grams, typically greater than or equal to 10 seconds/50 grams, and more typically greater than or equal to 12 seconds/50 grams. The Hall flow values of the particulate composition may range between any combination of these upper and lower values, inclusive of the recited values. For example, the particulate composition of the present invention may have a Hall flow value of from 8 to 35 seconds/50 grams, typically from 10 to 30 seconds/50 grams, and more typically from 12 to 25 seconds/50 grams.

The particles of the particulate composition may have irregular and/or regular shapes (e.g., rod-like, elongated and/or spherical shapes). Preferably, the particles of the particulate composition each have a shape that is substantially spherical (e.g., having generally spherical and/or ellipsoidal shapes). A substantially spherical shape enhances the handling of the particulate compositions (e.g., by providing improved flowability).

The particulate composition of the present invention may have a wide range of average particle sizes. The average particle size of the particulate composition may be selected, for example, for purposes of enhancing handling and use thereof during the production of molded articles (e.g., frangible projectiles) there from. The particulate composition may have an average particle size of from 25 to 300 μm, typically from 38 to 250 μm, and more typically from 45 to 180 μm. The average particle size of the particulate composition of the present invention may be determined in accordance with ASTM B 214, using for example a Ro-Tap sieve shaker, commercially available from Laval Lab, Inc.

Particulate compositions according to the present invention are preferably substantially free of: the first metal being coated and/or encapsulated by the second metal; and the second metal being coated and/or encapsulated by the first metal. By coated and/or encapsulated is meant that one metal (e.g., the second metal) forms a substantially continuous layer around a core comprising the other metal (e.g., the first metal). For example, when the first metal is tungsten, and the second metal is tin, the tungsten particles of the particulate composition are substantially free of being coated and/or encapsulated with tin; and the tin particles are substantially free of being coated and/or encapsulated with tungsten. While it is possible for particles of one metal (e.g., the second metal) to surround and/or abut one or more particles of the other metal (e.g., the first metal), such an association or agglomeration of metal particles is not deemed to be or to represent a coating or encapsulation of the abutted and/or surrounded metal particle(s).

The particulate compositions of the present invention may be prepared by methods that include, but are not limited to bulk mixing and granulation methods, and spray drying. Bulk mixing and granulation methods typically include preparing a bulk mixture of the first metal, optionally the second metal and the binder, and then granulating the bulk mixture (e.g., in a hammer mill or a jet mill). Preparation of the bulk mixture may be achieved by means of, for example, extrusion or driving an organic solvent off of a mixture of the metals, binder and organic solvent.

In a preferred embodiment of the present invention, the particulate composition is prepared by spray drying. The first step in the spray drying process involves the preparation of a substantially homogenous particulate metal mixture, which comprises separate particles of the first metal and optionally the second metal. The first and second metals each being selected from those metals as recited previously herein. The particulate metal mixture is a substantially dry particulate metal mixture (i.e., it is substantially free of liquids such as water and/or organic solvents). However, the particulate metal mixture may contain small amounts of water as the result of ambient humidity. The substantially homogenous particulate metal mixture may be prepared by means that are known to the skilled artisan, for example, using rotary mixers and/or shaker mixers.

The first metal is present in the substantially homogenous particulate metal mixture in an amount of less than or equal to 100 percent by weight, typically less than or equal to 95 percent by weight, and more typically less than or equal to 90 percent by weight, based on the total weight of the particulate metal mixture. The first metal also is present in the substantially homogenous particulate metal mixture in an amount of greater than or equal to 30 percent by weight, typically greater than or equal to 50 percent by weight, and more typically greater than or equal to 65 percent by weight, based on the total weight of the particulate metal mixture. The first metal may be present in the particulate metal mixture in an amount ranging between any of these upper and lower values, inclusive of the recited values. For example, the first metal may be present in the particulate metal mixture in an amount of from 30 to 100 percent by weight, typically from 50 to 95 percent by weight, and more typically from 65 to 90 percent by weight, based on the total weight of the particulate metal mixture.

The second metal is present in the substantially homogenous particulate metal mixture in an amount of less than or equal to 70 percent by weight, typically less than or equal to 50 percent by weight, and more typically less than or equal to 35 percent by weight, based on the total weight of the particulate metal mixture. The second metal also is present in the substantially homogenous particulate metal mixture in an amount of greater than or equal to 0 percent by weight, typically greater than or equal to 5 percent by weight, and more typically greater than or equal to 10 percent by weight, based on the total weight of the particulate metal mixture. The second metal may be present in the particulate metal mixture in an amount ranging between any of these upper and lower values, inclusive of the recited values. For example, the second metal may be present in the particulate metal mixture in an amount of from 0 to 70 percent by weight, typically from 5 to 50 percent by weight, and more typically from 10 to 35 percent by weight, based on the total weight of the particulate metal mixture.

In the next step of the spray dry method of the present invention, a slurry comprising the homogenous particulate metal mixture, water, binder and optionally a defoamer, is prepared. The slurry may be prepared by adding the components thereof together in any order. Preferably, the binder, water and optional defoamer are first mixed together, and then the particulate metal mixture is added thereto, typically with constant agitation (e.g., as may be provided by an impeller or circulating pump). The binder may be selected from those binders as recited previously herein.

The slurry may contain the first metal in an amount of from 24 to 89 percent by weight, typically from 41 to 84 percent by weight, and more typically from 55 to 78 percent by weight, based on the total weight of the slurry. The second metal may be present in the slurry in an amount of from 0 to 63 percent by weight, typically from 4 to 44 percent by weight, and more typically from 8 to 30 percent by weight, based on the total weight of the slurry. The binder may be present in the slurry in an amount of from 0.4 to 2.2 percent by weight, typically from 0.5 to 1.1 percent by weight, and more typically from 0.6 to 0.9 percent by weight, based on the total weight of the slurry.

The defoamer may be present in the slurry in an amount effective to minimize and preferably prevent the formation of foam in the slurry. Typically it is desirable to use only as much defoamer as is necessary to achieve a desired level of minimal foaming. The defoamer may be present in the slurry in an amount of from 0 to 0.05 percent by weight, typically from 0.02 to 0.04 percent by weight, and more typically from 0.025 to 0.035 percent by weight, based on the total weight of the slurry.

The defoamer may be selected from those classes and types of defoamers that are known to the skilled artisan for use in aqueous systems. For example, the defoamer may be selected from silicones, alkylene glycols, poly(alkylene glycols), and combinations and mixtures thereof.

The slurry may optionally further include organic solvents or cosolvents. Organic solvents may be present in the slurry in amounts that are typically less than 20 percent by weight, and more typically less than 10 percent by weight (e.g., from 1 to 20 percent by weight or from 2 to 10 percent by weight), based on the total weight of the slurry. Organic solvents that may be present in the slurry include, but are not limited to alcohols, ethers, esters and mono-ether glycols. Alcohols that may optionally be present in the slurry include, but are not limited to: linear or branched C₁-C₁₈ alkanols, such as methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, t-butanol, n-pentanol, i-pentanol, hexanol, heptanol, octanol, nonanol, decanol, dodecanol, undecanol, dodecanol, tridecanol, tetradecanol, pentadecanol, hexadecanol, heptadecanol and octadecanol; cycloaliphatic alcohols having from 5 to 8 carbons in the cyclic ring, e.g., cyclopentanol, cyclohexanol, cycloheptanol and cyclooctanol; and aromatic alcohols optionally substituted with one or more linear or branched C₁-C₁₀ alkyl groups, such as phenol and nonyl phenol. Ethers that may be present in the slurry include, but are not limited to, symmetric and asymmetric linear or branched C₁-C₈ dialkyl ethers, such as diethyl ether and t-butyl ethyl ether. Esters that may be present in the slurry include, but are not limited to, linear or branched C₁-C₁₈ alkyl esters of linear or branched C₁-C₁₈ carboxylic acids, such as ethyl acetate and ethyl ester of octadecanoic acid. Mono-ether glycols that may be present in the slurry include, but are not limited to, linear or branched C₁-C₈ mono-ethers of C₂-C₅ alkylene glycols, such as ethylene glycol mono-butyl ether and ethylene glycol mono-hexyl ether.

The slurry may optionally include surfactants other than defoamers. In an embodiment, the slurry further comprises one or more surfactants selected from anionic surfactants, amphoteric surfactants and non-ionic surfactants. Such surfactants may be selected from those that are known to the skilled artisan. Surfactants may be present in the slurry in amounts less than or equal to 10 percent by weight, and more typically less than or equal to 5 percent by weight, based on the total weight of the slurry.

Examples of anionic surfactants that may be used in the present invention include, for example, amine salts or alkali salts of carboxylic, sulfamic or phosphoric acids, for example sodium lauryl sulfate, ammonium lauryl sulfate, lignosulfonic acid salts, and ethylene diamine tetra acetic acid (EDTA) sodium salts. Amphoteric surfactants that may be present in the slurry include, for example: lauryl sulfobetaine; dihydroxy ethylalkyl betaine; amido betaine based on coconut acids; disodium N-lauryl amino propionate; or the sodium salts of dicarboxylic acid coconut derivatives. Examples of non-ionic surfactants that may be included in the slurry include, poly(C₂-C₄ alkoxylated) C₁₄-C₁₈ unsaturated fatty acids, poly(C₂-C₄ alkoxylated) phenol and poly(C₂-C₄ alkoxylated) C₁-C₉ alkyl substituted phenol.

After preparing the slurry, it is then passed through a spray drying apparatus. Spray drying apparatuses that may be used in the method of the present invention typically include a spray device that is selected from, for example, single fluid nozzles, dual fluid nozzles, rotary atomizers and combinations thereof. The spray drier is typically fitted with a collection system, which may include filters and/or a rotary sieve. The slurry may optionally be continually agitated in a container (such as a holding tank), from which it is drawn and fed through the spray drier.

The feed rate, and inlet and outlet temperatures under which the spray drier is operated are selected such that the water and optional organic solvents and cosolvents of the slurry passed there-through are driven off, and a particulate composition according to the present invention is produced. In an embodiment of the present invention, the inlet temperature of the spray drier may be from 200° C. to 300° C., typically from 220° C. to 280° C., and more typically from 240° C. to 270° C. The outlet temperature of the spray drier may be from 100° C. to 165° C., typically from 115° C. to 160° C., and more typically from 130° C. to 155° C.

When prepared by spray drying, the particles of the particulate composition are typically substantially spherical having shapes selected, for example, from generally spherical shapes, elongated shapes and/or ellipsoidal shapes. The surface of the spray dried particles may be smooth, but are more typically rough or bumpy in appearance, as observed in photomicrographs having a resolution of approximately 1 μm.

Molded articles prepared from the particulate compositions of the present may be sintered or non-sintered. Molded articles may be prepared from the particulate compositions of the present invention by means that are known to the skilled artisan, such as cold pressing, hot pressing or melt molding. In a preferred embodiment, molded articles are prepared from the particulate compositions of the invention by means of cold pressing/molding, which typically involves applying elevated pressures to an amount of particulate composition within a mold at ambient temperature (e.g., from 25° C. to 30° C.). Elevated pressures that may be used during cold pressing of the particulate composition are typically in excess of 1000 pounds per square inch (psi) (70 Kg/cm²), e.g., 2000 psi (140 Kg/cm²), 5000 psi (352 Kg/cm²), 10,000 psi (703 Kg/cm²), 15,000 psi (1055 Kg/cm²) or 20,000 psi (1406 Kg/cm²). The application of pressure during the cold pressing process may be done by means of ramping (up and/or down) and/or in stages (up and/or down), and for a period of time at least sufficient to form a non-sintered and frangible molded article, such as a frangible bullet (e.g., from a few seconds up to 60 minutes, depending for example on the size and dimensions of the molded article).

Molded articles that may be prepared from the particulate compositions of the invention include, but are not limited to, projectiles (e.g., bullets), and casings or housings for explosive charges, such as shells, cluster bombs, grenades (e.g., fragmentary grenades) and mines (e.g., anti-personnel mines). In a preferred embodiment, molded articles prepared from the particulate compositions of the invention are substantially non-sintered and are frangible. Frangible and non-sintered molded articles that may be prepared from the particulate compositions of the present invention include, but are not limited to frangible projectiles, such as frangible bullets, and frangible casings or housings for explosive charges, including those examples as recited previously herein.

Molded articles, such as frangible projectiles, prepared from the particulate compositions of the invention may have a wide range of densities. The density of the molded article may be controlled in part by selecting: the types and ratios of metals that are used to prepare the particulate composition; the amount of particulate composition introduced into the mold cavity; and the pressures used to prepare the molded article. In a preferred embodiment, the molded article is a substantially non-sintered and frangible projectile (e.g., a frangible bullet) having a density approximating that of a lead projectile or bullet, for example, having a density of from 11.0 to 11.5 g/cm³, or from 11.2 to 11.4 g/cm³, such as 11.3 g/cm³.

The present invention is more particularly described in the following examples, which are intended to be illustrative only, since numerous modifications and variations therein will be apparent to those skilled in the art. Unless otherwise specified, all parts and percentages are by weight.

EXAMPLES Example A Preparation of Particulate Metal Mixture

A particulate metal mixture was prepared by mixing 5443 grams of particulate tungsten (having an average particle size of 5 μm), and 1361 grams of particulate tin (having an average particle size of 12 μm) in a TURBULA shaker-mixer (available commercially from Glenn Mills, Inc.). The particulate tungsten and tin were mixed in the mixer for 20 minutes, and the resulting particulate metal mixture was determined to be substantially homogenously mixed by means of visual inspection. The particulate metal mixture of tungsten and tin was substantially dry and free flowing.

The average particle sizes of the particulate tungsten and particulate tin, from which the particulate metal mixture was prepared, were each determined in accordance with ASTM B 822. The particulate tungsten was obtained commercially from H.C. Stark Inc., and the particulate tin was obtained commercially from OMG Americas Inc.

Example B Preparation of Slurry

A slurry was prepared by mixing 5 grams of Antifoam 221 silicone-glycol emulsion (obtained commercially from Dow Corning Corporation) with 1270 grams of water, and then 91 grams of polyvinyl alcohol was added to the mixture of water and defoamer. The mixture of water, polyvinyl alcohol and defoamer was thoroughly mixed with an impeller. Next, 6803 grams of the particulate metal mixture of Example A was added to the mixture of water, polyvinyl alcohol and defoamer to form the slurry, which was continuously mixed using an impeller.

Example C Preparation of the Particulate Composition

The slurry of Example B, while continually being stirred with an impeller, was passed through a spray drier comprising a dual-fluid nozzle, at a rate of 907 grams/min. The spray drier was operated at an inlet temperature of 260° C. and an outlet temperature of 149° C.

The particulate composition resulting from the spray drying operation had: an average particle size of 75 μm (as determined in accordance with ASTM B 214); a Hall flow of less than 25 seconds/50 g (as determined in accordance with ASTM B 213); and an apparent density of approximately 4 g/cm³ (as determined in accordance with ASTM B 329).

Example D Preparation of Frangible Bullets

Frangible bullets according to the present invention (of various sizes, including 0.40 calibre, 0.45 calibre and 9 mm bullets) were prepared from the particulate composition of Example C in an automated mechanical press (model MPA6.XS, commercially available from ATLASpress Manfred Pscherer GmbH via Precision Rebuilders, Inc.) at ambient room temperature and under a pressure of 10,000 psi (703 Kg/cm²).

The frangible bullets of Example D were substantially non-sintered frangible bullets, and were determined to have a green strength at least sufficient to allow them to be swaged into a copper jacket without fracturing. In addition the frangible bullets of Example D were found to have a density of 11.4 g/cm³.

Hand gun and rifle tests were conducted using the frangible bullets of Example D. The frangible bullets of Example D were found to exit the gun barrel without breaking up, and were also found to be frangible upon hitting gypsum board (dry-wall), in sub-sonic and supersonic muzzle velocity firing tests.

Frangible bullets of equivalent sizes (e.g., 0.40 calibre) prepared in accordance with Example D, were found to have minimal variation in weight, density, and trajectory and frangibility in firing tests.

Attempts to prepare frangible bullets using the particulate mixture of Example A directly, resulted undesirably in clogging of the feed port of the automated mechanical press, and unacceptable variations in bullet weights.

The present invention has been described with reference to specific details of particular embodiments thereof. It is not intended that such details be regarded as limitations upon the scope of the invention except insofar as and to the extent that they are included, in the accompanying claims. 

1. A particulate composition comprising: (a) a first metal selected from the group consisting of tungsten, tungsten carbide, ferro-tungsten, bismuth, stainless steel, tantalum, molybdenum, combinations thereof, and alloys of at least two metals thereof, said first metal having an average particle size of less than or equal to 10 μm; (b) optionally a second metal selected from the group consisting of tin, zinc, iron, copper, aluminum, combinations thereof, and alloys of at least two metals thereof, said second metal having an average particle size of less than or equal to 20 μm; (c) a binder selected from the group consisting of thermosetting resins, thermoplastic resins and combinations thereof, wherein each particle of said particulate composition substantially comprises, said first metal in an amount of from 30 percent by weight to 99 percent by weight, based on the total weight of said particulate composition, said second metal in an amount of from 0 percent by weight to 70 percent by weight, based on the total weight of said particulate composition, and said binder in an amount of 0.5 percent by weight to 2.5 percent by weight, based on the total weight of said particulate composition, said particulate composition has an average particle size of from 25 μm to 300 μm, and said particulate composition is substantially free flowing.
 2. The particulate composition of claim 1 wherein the particles of said particulate composition are substantially spherical.
 3. The particulate composition of claim 1 wherein said first metal comprises tungsten, and said second metal comprises tin.
 4. The particulate composition of claim 1 wherein said binder is a thermoplastic resin selected from the group consisting of polyvinyl alcohol, poly(C₂-C₅-alkylene glycol), hydroxyalkylcellulose, polyacrylate, polymethacrylate, polyurethane, polyolefin, polyester, polyamide and combinations thereof.
 5. The particulate composition of claim 1 wherein said first metal is tungsten, said second metal is tin, said binder is thermoplastic polyvinyl alcohol, and said particles of said particulate composition are substantially spherical.
 6. The particulate composition of claim 5 wherein said particulate composition has a tungsten to tin weight ratio of 4 to
 1. 7. A method of preparing a particulate composition comprising: (a) forming a substantially homogenous particulate metal mixture comprising, (i) a first metal selected from the group consisting of tungsten, tungsten carbide, ferro-tungsten, bismuth, stainless steel, tantalum, molybdenum, combinations thereof, and alloys of at least two metals thereof, said first metal having an average particle size of less than or equal to 10 μm, and (ii) optionally a second metal selected from the group consisting of tin, zinc, iron, copper, aluminum, combinations thereof, and alloys of at least two metals thereof, said second metal having an average particle size of less than or equal to 20 μm, said first metal being present in said particulate metal mixture in an amount of from 30 percent by weight to 100 percent by weight, based on the total weight of said particulate metal mixture, said second metal being present in said particulate metal mixture in an amount of from 0 percent by weight to 70 percent by weight, based on the total weight of said particulate metal mixture, and said particulate metal mixture being substantially dry; (b) preparing a slurry comprising, (i) said homogenous particulate metal mixture, (ii) water, (iii) a binder selected from the group consisting of thermosetting  resins, thermoplastic resins and combinations thereof, and (iv) optionally a defoamer, wherein said slurry contains, said first metal in an amount of from 24 to 89 percent by weight, based on the total weight of said slurry, said second metal in an amount of from 0 to 63 percent by weight, based on the total weight of said slurry, water in an amount of from 10 to 25 percent by weight, based on the total weight of said slurry, binder in an amount of from 0.4 to 2.2 percent by weight, based on the total weight of said slurry, and defoamer in an amount of from 0 percent by weight to 0.05 percent by weight, based on the total weight of said slurry; and (c) passing said slurry through a spray drier, thereby forming said particulate composition, wherein each particle of said particulate composition substantially comprises, said first metal in an amount of from 30 percent by weight to 99 percent by weight, based on the total weight of said particulate composition, said second metal in an amount of from 0 percent by weight to 70 percent by weight, based on the total weight of said particulate composition, and said binder in an amount of 0.5 percent by weight to 2.5 percent by weight, based on the total weight of said particulate composition, said particulate composition has an average particle size of from 25 μm to 300 μm, the particles of said particulate composition are substantially spherical, and said particulate composition is substantially free flowing.
 8. The method of claim 7 wherein said spray drier is operated at an inlet temperature of from 200° C. to 300° C., and an outlet temperature of 100° C. to 165° C.
 9. The method of claim 7 wherein said first metal comprises tungsten, and said second metal comprises tin.
 10. The method of claim 7 wherein said binder is a thermoplastic resin selected from the group consisting of polyvinyl alcohol, poly(C₂-C₅-alkylene glycol), hydroxyalkylcellulose, polyacrylate, polymethacrylate, polyurethane, polyolefin, polyester, polyamide and combinations thereof.
 11. The method of claim 7 wherein said first metal is tungsten, said second metal is tin, and said binder is thermoplastic polyvinyl alcohol.
 12. The method of claim 11 wherein said particulate composition has a tungsten to tin weight ratio of 4 to
 1. 13. The particulate composition prepared by the process of claim
 7. 14. A molded article comprising the particulate composition of claim
 13. 15. A molded article comprising the particulate composition of claim
 1. 16. The molded article of claim 15 wherein said molded article is substantially non-sintered, and said molded article is a projectile.
 17. The molded article of claim 16 wherein said projectile has a density of from 11.0 to 11.5 g/cm³.
 18. The molded article of claim 17 wherein said projectile is a frangible bullet. 